Bleach activators are important constituents in compact detergents, stain removal salts and dishwashing detergents. At from 40 to 60.degree. C., they permit a bleaching result which is comparable with a boil wash, by reacting with hydrogen peroxide donors (in most cases perborates or percarbonates) to release an organic peroxy acid.
The bleaching result obtainable depends on the nature and reactivity of the peroxycarboxylic acid formed, on the structure of the bond that is to be perhydrolyzed and on the solubility of the bleach activator in water. Since the activator is usually a reactive ester or an amide, it is frequently necessary to use it in granulated or coated form for the intended application area in order to prevent hydrolysis in the presence of alkaline detergent constituents and to ensure an adequate shelf life.
Numerous auxiliaries and processes have been proposed in the past for granulating these substances. EP-A-0 037 026 describes a process for producing readily soluble activator granules comprising between 90 and 98% by weight of activator. For this purpose, the pulverulent bleach activator is homogeneously mixed with likewise pulverulent cellulose ethers or starch ethers and then sprayed with water or an aqueous solution of the cellulose ether, simultaneously granulated and then dried.
According to EP-A-0 070 474, it is possible to prepare similar granules by spray drying aqueous suspensions comprising the activator and the cellulose ether. Granules consisting of bleach activator, cellulose ethers and additives of an organic C.sub.3 -C.sub.4 -carboxylic or hydroxycarboxylic acid are described in WO 90/01535 and WO 92/13798. While in WO 90/01535, the organic carboxylic acid is incorporated into the granule core in order to accelerate its solubility, in WO 92/13798, the carboxylic acid is deposited on the finished granule in an additional coating stage. The protective acid coating should prevent spotting of the bleach and contribute to preserving the color of the fabric. WO 94/03395 claims the use of acidic polymer compounds having a solubility in water of&gt;5 g/l (at 20.degree. C.) and molecular weights of from 1000 to 250 000 for the same purpose.
Granules of bleach activators in which mixtures of soaps and free fatty acids are used as granulating auxiliaries are likewise described (GB-A-1 507 312).
A waterless preparation process is known from EP-A-0 075 818. Here, the bleach activator, together with an organic binder, for example a fatty alcohol ethoxylate, is compressed by compaction under pressure to give particles having diameters of from 0.5 to 3 mm.
For most of these specified granulation processes, it is a prerequisite that the bleach activator to be granulated is a solid and has a high melting point. This is necessary in order that during preparation it does not react with the binder or water present and decompose. Thus, in DE-A 2 048 331, for example, preference is given to activators which have a melting point of preferably at least 100.degree. C., in particular at least 150.degree. C.
The binders which have hitherto been used are predominantly organic compounds.
This can, however, cause problems which limit the use of the granules.
If surface-active compounds are used, such as soaps, fatty acids, anionic surfactants or fatty alcohol ethoxylates, then the granules prepared therewith are unsuitable for use in dishwashing detergents since problems with foam arise under the washing conditions. This is even the case when normally low-foam highly ethoxylated fatty alcohols are used. For use in dishwashing detergents, therefore, activator granules whose binder consists of cellulose ethers are predominantly used. The biodegradability of this group of products is, however, moderate.
A further problem relates to suitable granules for stain removal salts. Modern formulations consist of mixtures of percarbonate and TAED granules. In order to prevent exothermic decomposition of these mixtures (percarbonate as a combustion-promoting substance in combination with organic material) during preparation and storage, inert materials, such as sodium carbonate, sodium hydrogencarbonate or sodium sulfate are frequently added. For this field of application, inert binders or coating agents would be of great interest.
There therefore continues to be a need for suitable activator granules which are without problems from an ecological point of view, can be used universally and can be prepared at favorable cost.
Inorganic materials as carriers for bleach activators are known per se. For example, DE-A 2 733 849 proposes the adsorption of liquid activators, such as diacetylmethylamine, diacetylbutylamine or acetal caprolactam on inorganic adsorbants, such as kieselguhr, magnesium aluminum silicates, sodium or calcium aluminum silicates, activated silica or aluminum oxide. Granules are not, however, described therein.
Furthermore, according to GB-A 2 249 104, it is possible to prepare particles in which a bleach activator solid per se is deposited in finely divided form on an inorganic carrier material. For this purpose, activator and carrier material are firstly intimately mixed, and an organic solvent (ethanol or toluene) is added, as a result of which the activator goes into solution. By subsequently distilling off the solvent, the activator is deposited in very finely divided form on the carrier. The preferred particle size distribution of the particles according to the invention is between 60 and 250 .mu.m.
In addition, EP-A-0 240 057 discloses bleach activator granules which are prepared by mixing an activator with inorganic and organic salts, film-forming polymers and small amounts of smectites or aluminum silicates and subsequently granulating the mixture in the presence of water. Once granulation is complete, a costly drying stage is necessary in order to obtain storage-stable granules.
DE-A 44 39 039 describes a water-free and solvent-free granulation process in which the binders used are bentonites, in particular bentonites which have been activated to be alkaline.